Recently, display technologies using various methods such as a plasma display panel (PDP), a liquid crystal display (LCD) and the like that are used instead of a known brown tube in accordance with the development of optical technologies are suggested and sold. The higher properties of the polymer material for displays are required. For example, in the case of the liquid crystal display, according to the development toward the thin film, the lightness, and enlargement of the screen area, the wide viewing angle, the high contrast, the suppression of change in image color tone according to the viewing angle and the uniformity of the screen display are particularly considered as important problems.
Therefore, various polymer films such as a polarizing film, a retardation film, a plastic substrate, a light guide plate and the like are used, and various modes of liquid crystal displays such as twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS) liquid crystal cells are developed. Since all of these liquid crystal cells have intrinsic liquid crystal alignment, they have intrinsic optical anisotropic property, and in order to compensate the optical anisotropic property, a film in which a retardation function is provided by stretching various kinds of polymers has been suggested.
In detail, since a liquid crystal display device uses high birefringence property and alignment of liquid crystal molecules, the birefringences are different according to the viewing angle and thus the color and brightness of the picture are changed. For example, since most liquid crystal molecules that are used in a vertical alignment method have a positive retardation in a liquid crystal display surface, in order to compensate this, a compensation film that has a negative retardation is required. In addition, light does not pass through the front sides of two polarizing plates that are perpendicular to each other, but if the angle is inclined, the light axes of two polarizing plates are not perpendicular to each other, thus light leakage occurs. In order to compensate this, a compensation film having the in-plane retardation is required. In addition, display devices using a liquid crystal require both thickness retardation compensation and in-plane retardation compensation in order to widen the viewing angle.
Requirements of the retardation compensation film are to control the birefringence easily. However, the film birefringence is formed by a basic birefringence which belongs to the material and the orientation of polymer chains in the film. The orientation of the polymer chains is mostly forcibly performed by force applied from the outside or is caused by the intrinsic properties of the material, and the orientation method of the molecules by the external force is to stretch a polymer film uniaxially or biaxially.
In order to solve viewing angle problems of LCDs due to intrinsic birefringence properties of the liquid crystal, N-TAC, V-TAC, and COP Films have been recently used as a compensation film or a retardation film. However, these films are expensive and have problems in that processes are complicated during the manufacture of the films.